This application claims the priority of German application 197 05 414.5-14 filed in Germany on Feb. 13, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a pneumatic control unit for at least partial opening of a movable body part of a motor vehicle, with a control member that is linearly movable along a control axis and projects partially out of a housing, said member being capable of being pressurized by a working chamber provided in the housing, with the free end of said member being provided with a contact surface for abutting the movable body part, with said body part exerting a contact pressure on the contact surface of the control member in a closed resting position.
A pneumatic control unit is known from German Patent Document DE 44 27 148 A1, said unit being provided both for actuating a central locking system and as a pulling aid for pulling a movable body part out of a previously latched position into a closed position. For this purpose the pneumatic control unit has two drive members mounted coaxially with respect to one another, said members being movable separately or jointly by different pressure applications.
A goal of the invention is to use a simple pneumatic device to open the movable body part and to allow a simple return of the control unit to the initial position.
This goal is achieved in accordance with preferred embodiments of the invention by providing a pneumatic drive unit for at least partial opening of a movable body part of a motor vehicle with a control member that is linearly movable along a control axis, said member partially extending out of a housing, said member being capable of being pressurized by means of a working chamber provided in the housing, and with a free end of said member being provided with a contact surface for abutting the movable body part, with the body part, in a closed resting position, exerting a contact pressure on the contact surface of the control member, wherein a vent channel is provided that connects the working chamber with the atmosphere, and wherein a closing element is provided that is loaded by a spring arrangement for closing and opening the vent channel, said closing element being held in its closed position when the body part rests on the contact surface of the control member, and when the body part is removed from the contact surface by the spring force of the spring arrangement can be moved into its open position to open the vent channel.
Embodiments of the invention are advantageous in that a vent channel connecting the working chamber with the atmosphere is provided in the control member, with which channel a closing element for closing and opening said vent channel is associated, said closing element being loaded by a spring arrangement, with the closing element being held in its closed position when the body part abuts the contact surface of the control member, and being movable into its opening position that opens the vent channel when the body part is moved away from the contact surface by the spring force of the spring arrangement.
Pressurizing the working chamber forces the control member out of the housing, so that the movable body part is simultaneously moved out of a closed resting position. Advantageously a rear body part in the form of a trunk lid is provided as the body part, so that opening the body part constitutes lifting the body part. The pneumatic control unit is especially advantageous in conjunction with remote unlocking of the rear body part, since the lifting of the rear body part creates a gap between the edge of the trunk and the lower edge of the rear body part, which makes it readily apparent that the rear body part is in an open position. If the rear body part is not lifted by the control unit, although the rear body part is unlocked, it is possible that the unlocked state of the rear body part will not be detected. The provision of the vent channel in conjunction with the closing element according to the invention permits the control member to be charged with air and thus returned together with the closing element into the initial position, as soon as the body part separates from the contact surface of the control member, in other words in particular as soon as the rear body part is lifted off the contact surface. Such lifting out of the already partially open position of the body part can be accomplished manually or by a gas compression spring or a similar control element.
In an embodiment of the invention, the closing element is designed as a closing piston mounted to be linearly movable coaxially to the control axis in a cavity of the control member that is open to the contact surface, said piston being provided with a seal for sealing the vent channel. This is an especially sturdy and functionally reliable design.
According to another aspect of preferred embodiments of the invention, the closing piston forms an annular chamber with a wall of the cavity, said chamber constituting a part of the vent channel, and the annular chamber is connected by a channel section with the working chamber. As a result, the working chamber is rapidly charged with air and, as a result, the control member is rapidly returned to its initial position.
According to another aspect of preferred embodiments of the invention, the annular chamber has at least one vent opening that projects radially through the wall of the control member, relative to the control axis, and the closing piston has an annular seal that seals off the annular chamber, said seal being located in the closed position of the closing piston on a wall of the annular chamber that faces the working chamber.
According to another aspect of preferred embodiments of the invention, the stroke of the closing piston that is triggered by the spring force of the spring system is dimensioned relative to the control member in such fashion that the annular seal is on a side of the vent opening that faces the contact surface when the closing piston is in the open position. By a simple linear displacement of the closing piston therefore the vent channel is opened for charging the working chamber with air, so that the stroke of the closing piston necessarily takes place together with the lifting of the body part from the contact surface of the control member, so that the closing piston is forced out by means of the spring force of the spring system, partially upward out of the cavity of the control member.
According to another aspect of preferred embodiments of the invention, the working chamber can be shut off by a check valve located between a connecting stub of the housing and the working chamber. As a result, it is possible to trap the pressure for actuating the control member in the working chamber, so that the pressure in the working chamber is maintained even when the rest of the pneumatic system to which the drive unit is connected has already been vented.
According to another aspect of preferred embodiments of the invention, the spring force of the spring arrangement is less than the contact pressure of the body part. Therefore, as soon as the body part is re-closed and comes to rest on the contact surface of the control member, the closing piston is forcibly pushed back into its initial position in which it is recessed in the control member.
According to another aspect of preferred embodiments of the invention, a compression spring is associated with the control member, said spring restoring the control member to the resting position. Therefore, as soon as the working chamber has been vented, this compression spring pushes the control member back into the initial position.
According to another aspect of preferred embodiments of the invention, the contact surface is formed by a contact plug that covers both the control member and the closing piston, said plug also being provided with a compensating sleeve to accept a relative movement between the closing piston and the control member. As a result the extension of the closing piston relative to the control member under the spring force of the spring arrangement is not impeded by the contact plug. The contact plug is preferably made of an elastic material, with the compensating sleeve being made integral with the contact plug. The elastic material prevents a hard impact of the body part against the contact surface.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.